Re: database design method

From: Lauri Pietarinen <lauri.pietarinen_at_atbusiness.com>
Date: Sat, 16 Nov 2002 08:47:20 +0200
Message-ID: <3DD5E9F8.C50E298B@atbusiness.com>

> >However, here is an example of a recursive operator expressed in Tutorial-D
> >(page 163, 2ed):
> >
> >OPERATOR TRANCLO ( XY RELATION { X P#, Y P# } )
> > RETURNS RELATION { X P#, Y P# } ;
> > RETURN
> > WITH ( XY UNION ( ( XY COMPOSE
> > ( XY RENAME ( Y AS Z, X AS Y ) ) )
> > RENAME Z AS Y ) ) AS TTT :
> > IF TTT = XY THEN TTT /* unwind recursion */
> > ELSE TRANCLO ( TTT ) /* recursive invocation */
> > END IF;
> > END OPERATOR;

>
> Wow. That's a pretty powerful type of recursion. It will be interesting to
> see how well query optimization for such recursive expressions will perform
> once this gets really implemented.

Well, they also go on to say that

"We make no claim that TRANCLO is very efficcient but it surely can be improved in this regard"

> Dataphor has this I presume?

I think they do not yet support relation valued operators.

regards,
Lauri Pietarinen Received on Sat Nov 16 2002 - 00:47:20 CST